Conventionally, as shown in FIG. 12, proposed is an infrared sensor which houses, in a can package 130, a pyroelectric element 101, an IC device 102 in which most of the signal processing circuit that signal-processes an output current of the pyroelectric element 101 is integrated onto one chip, and a three-dimensional circuit block 120 made from an MID (Molded Interconnect Devices) substrate mounted with a capacitor (not shown) and the like attached outside the IC device 102 (for example, refer to Japanese Patent Publication No. 3367876; hereinafter referred to as “Patent Document 1”). Here, with the MID substrate configuring the three-dimensional circuit block 120, a circuit pattern 122 is formed on a surface of a resin molding 121. Moreover, the can package 130 is configured from a metal stem 131, and a metal cap 132 having an optical filter window 132a. Moreover, with the infrared sensor shown in FIG. 12, a dome-shaped condenser lens 150 is mounted outside the can package 130.
Moreover, conventionally, in an infrared sensor which houses, in a can package, a pyroelectric element and an IC device (signal processing IC) which processes an output signal of the pyroelectric element, it is known that the sensitivity will deteriorate when the signal input terminal and the signal output terminal of the IC device are subject to capacitive coupling (for example, refer to Japanese Patent Publication No. 4258139; hereinafter referred to as “Patent Document 2”). Here, foregoing Patent Document 2 discloses an infrared sensor in which, as shown in FIG. 13 and FIG. 14, a pyroelectric element 201 is mounted on an upper face part of a simultaneously-formed molding 210 in which first to seventh metal members 211 to 217 are insert-molded, an IC device 202 is mounted on a front face part of the simultaneously-formed molding 210, and an external capacitor C1 is mounted on a side face part of the simultaneously-formed molding 210. In addition, with this infrared sensor, in order to reduce the foregoing capacitive coupling, the fourth metal member 214 is bent as a metal member that is used exclusively for shielding, and the first metal member 211 for internal wiring that is connected to a signal input terminal and the sixth metal member 216 for external wiring that is connected to a signal output terminal are disposed in a diagonal direction relative to the simultaneously-formed molding 210. Moreover, the package 230 of this infrared sensor is configured from a metal stem (metal base) 231 mounted with the simultaneously-formed molding 210, and a metal cap 232, and a cap 232 is provided with an infrared transmission filter 233.
The IC device 102 disclosed in foregoing Patent Document 1 comprises, for example, a current-voltage conversion circuit, a voltage amplifier circuit, and an output circuit. The current-voltage conversion circuit comprises an operating amplifier in which a feedback capacity (capacitor) is connected between an inverting input port and an output port and a reference voltage is supplied from a non-inverting input port to a power circuit. A pyroelectric element is connected to the inverting input port of the operating amplifier so as to input pyroelectric current, and a small pyroelectric current is converted into a voltage signal of roughly several 10 μV based on the impedance conversion of the capacitor. With this current-voltage conversion circuit, it is possible to attenuate the impact of thermal noise, which is considered the dominant factor in a conventional current-voltage conversion circuit made of an impedance conversion circuit using a field-effect transistor and resistance of a high resistance value, considerably improve the S/N ratio, and thereby reduce noise and improve the sensitivity.
Nevertheless, with the infrared sensor configured as shown in FIG. 12, it is difficult to achieve a thin profile (low profile) since the three-dimensional circuit block 120 is housed in the can package 130, and, furthermore, surface mounting is not possible when the infrared sensor is to be secondarily mounted on a circuit board such as a printed-wiring board. Moreover, also with the infrared sensor configured as shown in FIG. 13, it is difficult to achieve a thin profile (low profile) since the simultaneously-formed molding 210 is housed in the can package 230, and, furthermore, surface mounting is not possible when the infrared sensor is to be secondarily mounted on a circuit board such as a printed-wiring board.
Meanwhile, proposed is an infrared sensor comprising, as shown in FIG. 15 and FIG. 16, a surface-mounted package 303 which houses an infrared sensor element 301, a field-effect transistor 302, a bypass capacitor (not shown), a resistor (not shown) having a high resistance value and the like, and an optical filter 304 mounted on an opening 303b of the package 303 (for example, refer to International Publication No. 2006/120863; hereinafter referred to as “Patent Document 3”).
With the infrared sensor disclosed in foregoing Patent Document 3, the package 303 is formed in a rectangular box shape in which one face thereof is open, and a plurality of bases 312 for supporting the infrared sensor element 301 are disposed on an inner bottom face of the package 303. In addition, the field-effect transistor 302, the bypass capacitor, the resistor and the like are arranged in parallel to the infrared sensor element 301. Moreover, the planar shape of the optical filter 304 is a rectangular shape which substantially corresponds to the opening 303b of the package 303. Specifically, the planar size of the optical filter 304 is set so as to form a gap between the side edge of the optical filter 304 and an inner side face of the package 303, and the optical filter 304 is supported by supports 320 that are respectively disposed at the four corners of the opening 303b of the package 303. In addition, the optical filter 304 and the metal package body 303a of the package 303 are bonded by a conductive adhesive and thereby electrically connected.
Meanwhile, with the infrared sensor configured as shown in FIG. 15 and FIG. 16, there is a limit to the improvement of the S/N ratio since the thermal noise that is generated by the resistor having a high resistance value will increase. Thus, in order to achieve high sensitivity, considered may be using an IC device 102 (refer to FIG. 12) or an IC device 202 (refer to FIG. 13), which can amplifying the weak output signal of the infrared sensor element 301 with a high gain, in substitute for the field-effect transistor 302, the bypass capacitor, the resistor and the like.
Nevertheless, in the foregoing case, since the infrared sensor element 301 and the IC device 102 or the IC device 202 need to be arranged in parallel next to each other in the package 303, it is difficult to achieve downsizing and cost reduction. Moreover, in the foregoing case, the sensitivity will deteriorate due to the capacitive coupling of the infrared sensor element 301 and the output wiring connected to the IC device 102, 202.